1. Field of the Invention
The present invention relates to preparation of mixtures rich in 2,3,5-trichloropyridine by non-catalytic chlorination of 3,5-dichloro-2-trichloromethyl pyridine in the absence of ultraviolet (UV) radiation. 2,3,5-trichloropyridine is useful as an intermediate for preparation of agricultural chemicals, especially herbicides.
2. Description of the Prior Art
Fah et al U.S. Pat. No. 4,287,347 describes a process for making 2,3,5-trichloropyridine by reacting 3,5-dichloro-2-pyridone with phosgene. Johnston et al U.S. Pat. No. 3,186,994 discloses the preparation of polychloropyridines by chlorination of chloro-2-trichloromethyl pyridines at temperatures in excess of 160.degree. C., but no mention is made of preparing 2,3,5-trichloropyridine by the process. According to this patent, chlorination of
3,5-dichloro-2-trichloromethyl pyridine at temperatures between 190.degree. C. and 210.degree. C. yields 2,3,5,6-tetrachloropyridine. In Johnston et al U.S. Pat. No. 3,418,323, a process for producing 2,3,5-trichloro-6-trichloromethyl pyridine is taught by chlorination of 3,5-dichloro-2-trichloromethyl pyridine at temperatures from 135.degree. C. to 145.degree. C.
Kosorotov et al, Zhurnal Organicheskoi Khimii, Vol. 16, pp. 2163-2171 (October 1980) appears to teach the production of 2,3,5-trichloropyridine by photochemical chlorination under UV irradiation of 3,5-dichloro-2-trichloromethyl pyridine at 150.degree. C. as a result of the elimination of CCl.sub.3 (dealkylation) with substitution by a chlorine atom.